In recent years, 3GPP has put a lot of efforts on standardization of the advanced LTE technology coordinated multipoint transmission or reception (CoMP). DL CoMP is CoMP operating in the downlink direction of an advanced LTE system. Since it can allow the system to be able to coordinate downlink data transmissions across multiple cells in a dynamic fashion, it greatly improves the system performance, including service coverage, cell-edge throughput, and spectrum efficiency. DL CoMP is especially useful at removing inter-cell interference (ICI) experienced by the served UEs and allows the MIMO technology to work in a high signal-to-interference-noise-ratio (SINR) region to exhibit its high gain performance.
It is well known that ICI is a major gating factor to limit the downlink performance of an LTE cellular network, particularly to the throughput of UEs located near the cell borders in the network. This is simply because ICI makes the downlink SINR level received by a UE down into the range where it is too low to keep the UE receiver working with good performance and this kind of bad channel condition becomes more severe at the cell borders than anywhere else in the network.
To mitigate ICI, three types of conventional technical methods can be used. The first type is to make use of the averaging technique to average out the ICI over a considerably long time period or a quite large frequency range. An example is the frequency hopping used by PUSCH, as specified in the LTE standard Release 8. This method is effective in some situations but too costly in some others where a tight constraint exits on time and frequency resources. The second type is viewed as the ICI cancellation technique which is usually used at the receiver side to reduce the ICI by utilizing the multi-user detection such as MMSE-SIC or some complex combining technique such as IRC. In general, the implementation complexity and costs of this type of methods are quite high, especially for the receiver of a handheld device which is required to remain simple in terms of signal processing power consumption. The third type is of the so-called ICI avoidance technique. The principle is to treat Sector-center UEs and Sector-edge UEs differently by statically assigning a common chunk of frequency band to all Sector-center UEs and a different chunk of frequency band to Sector-edge UEs in different sectors so as to avoid collisions of resource usage near the sector borders. The ICIC technique specified in LTE standard Release 8 is a typical example in this regard. However, the performance gain of this type of static fractional frequency reuse is still a concern.
For these reasons, traditional ICI mitigation methods have limited capabilities in situations as described above.